1. Field of the Invention
The present invention relates to an imaging device driver that controls the number of pixels to be mixed together by an imaging device which can carry out pixel mixing process and an auto focus unit that brings an object into focus based on an imaging signal generated by the imaging device controlling the number of pixels to be mixed.
2. Description of the Related Art
Many pixels are arranged on a light-receiving surface of an imaging device. Each pixel generates a pixel signal according to a received amount of light. By receiving an optical image of an object on an entire light-receiving surface, an image signal comprised of pixel signals created by some, if not all, of the pixels is generated.
A charge transfer type of imaging device, such as a CCD area sensor, has a plurality of pixels on its light-receiving surface. Each pixel generates a signal charge according to the received amount of light. In general, each individual signal charge is transferred and converted into a pixel signal that is a potential signal. During the transfer of the signal charge, the pixel mixing process is carried out by mixing signal charges generated by a plurality of pixels. By executing pixel mixing process for a plurality of pixels which are adjacent to each other and of the same color is, the sensitivity is raised and an optical image of a dark object can be captured with a higher sensitivity.
In general, some functions that are carried out by a digital camera based on a captured image do not work well with dark objects. However, by using pixel mixing process, such functions can be made to work accurately with dark objects.
On the other hand, when an optical image of a bright object is captured by a pixel mix processing system, or when an entire optical image which includes an optical image of a bright light source is captured by a pixel mix processing system, mixed signal charges became saturated because of the transfer capacity of the vertical and horizontal CCD. Accordingly, in such a case the accuracy of some functions, such as the auto focus function, deteriorates.